How-To

KJ Jones

January 2, 2014

This month we’re inspecting new technology for Ford’s latest leaders of the late-model-Mustang band, the ’13-’14 Shelby GT500s. With their big cubes (5.8-liter) and factory-installed superchargers, ’13-up Shelby engines are the baddest yet. It’s capable of making 600 crankshaft horsepower in stock configuration and tons more with mods.

An upgrade that’s quick, affordable, and guaranteed to make a positive difference on the latest GT500 is installing a smaller supercharger pulley. Decreasing the diameter of a blower’s drive pulley increases the unit’s speed, which increases boost. JMS Chip & Performance of Lucedale, Mississippi, has developed such a pulley—a 2.40-inch steel wheel that actually looks just like the stocker it replaces (because it’s made to actual OEM specifications).

The pulley (PN JMS-24-2013-SVT; $139.99) really has our interest, and Brotherman, one of the regulars at Addiction Motorsports in Canoga Park, California, has a brand-new, bone-stock ’13 Shelby that’s been left at our disposal for an experiment with basic boost. We followed Addiction’s Eddie Rios as he performed the standard pulley swap and remapped the GT500’s PCM using SCT tuning software.

As a rule of thumb for stock-Shelby owners planning on upgrades, introducing more air—especially boost—makes tuning the engine’s fuel trim crucial. Having such a procedure performed by a pro, like Eddie, on a chassis dyno is one of the best methods for ensuring maximum performance and engine efficiency. However, for DIY enthusiasts, JMS can accommodate your tuning needs with an optional handheld SCT flash tuner loaded with the appropriate custom calibration for the 2.40-inch pulley.

Photo Gallery

The smaller, JMS Chip & Performance blower pulley (PN JMS-24-2013-SVT; $139.99) and the supercharger’s increased speed were good for 2 pounds of peak boost, which generated over 20 additional peak horsepower, and more than 30 lb-ft of torque at the feet of our tester ’13 GT500. Note that our test was done on an absolutely stifling-hot day in Southern California, with ambient temperature in the dyno cell near 100 degrees.

With its required tuning, the stock-looking, 2.40-inch replacement GT500 blower pulley is impressive. However, complementing this upgrade with a larger Cobra Jet throttle body will really unleash a lot more power from an otherwise stock ’13-’14 Shelby.

STOCK

JMS

DIFFERENCE

RPM

Power

Torque

Boost

Power

Torque

Boost

Power

Torque

Boost

2,500

232.91

489.22

9.66

264.35

555.28

11.46

31.44

66.06

1.80

2,600

253.25

511.54

9.93

278.57

562.75

11.75

25.32

51.21

1.82

2,700

266.16

517.77

10.30

292.01

568.00

11.96

25.85

50.23

1.66

2,800

280.72

526.53

10.69

307.05

575.91

12.18

26.33

49.38

1.49

2,900

294.07

532.55

10.97

321.15

581.61

12.47

27.08

49.06

1.50

3,000

309.69

542.15

11.11

333.33

583.59

12.73

23.64

41.44

1.62

3,100

319.09

540.63

11.14

344.68

583.94

12.87

25.59

43.31

1.73

3,200

333.73

547.75

11.23

356.85

585.70

12.88

23.12

37.95

1.65

3,300

340.48

541.91

11.37

370.95

590.36

12.80

30.47

48.45

1.43

3,400

350.72

541.73

11.60

387.80

599.03

12.76

37.08

57.30

1.16

3,500

364.76

547.36

11.65

398.31

597.74

12.78

33.55

50.38

1.13

3,600

377.57

550.82

11.40

408.05

595.30

12.98

30.48

44.48

1.58

3,700

395.10

560.83

11.27

420.83

597.38

13.30

25.73

36.55

2.03

3,800

407.84

563.67

11.24

431.33

596.14

13.15

23.49

32.47

1.91

3,900

423.36

570.13

11.13

445.78

600.35

12.86

22.42

30.22

1.73

4,000

430.71

565.54

11.08

455.14

597.61

12.72

24.43

32.07

1.64

4,100

438.72

562.03

11.27

461.89

591.69

12.59

23.17

29.66

1.32

4,200

447.93

560.13

11.35

474.58

593.45

12.34

26.65

33.32

0.99

4,300

460.13

562.02

11.06

484.52

591.83

12.18

24.39

29.81

1.12

4,400

466.52

556.87

10.81

495.26

591.14

12.19

28.74

34.27

1.38

4,500

480.19

560.44

10.62

504.13

588.42

12.24

23.94

27.98

1.62

4,600

490.45

559.99

10.79

506.64

578.47

12.27

16.19

18.48

1.48

4,700

498.57

557.14

10.92

521.55

582.83

12.10

22.98

25.69

1.18

4,800

507.68

555.51

10.56

521.48

570.57

11.78

13.80

15.06

1.22

4,900

503.91

540.13

10.42

534.13

572.54

11.50

30.22

32.41

1.08

5,000

516.02

542.03

10.69

536.90

563.98

11.34

20.88

21.95

0.65

5,100

520.13

535.67

10.57

542.08

558.26

11.41

21.95

22.59

0.84

5,200

534.19

539.51

10.34

548.80

554.29

11.41

14.61

14.78

1.07

5,300

533.62

528.82

10.36

552.11

547.14

11.28

18.49

18.32

0.92

5,400

546.58

531.60

10.61

566.82

551.29

11.11

20.24

19.69

0.50

5,500

550.93

526.13

11.05

562.73

537.38

11.09

11.80

11.25

0.04

5,600

557.70

523.04

11.10

569.39

534.02

11.46

11.69

10.98

0.36

5,700

558.30

514.45

11.14

571.96

527.01

11.38

13.66

12.56

0.24

5,800

560.18

507.26

11.22

579.82

525.05

11.13

19.64

17.79

-0.09

5,900

564.06

502.13

11.26

580.95

517.19

11.20

16.89

15.06

-0.06

6,000

565.74

495.21

11.07

583.86

511.09

11.29

18.12

15.88

0.22

6,100

570.62

491.32

10.78

584.31

503.09

11.50

13.69

11.77

0.72

6,200

575.12

487.20

11.03

584.28

494.97

12.01

9.16

7.77

0.98

6,300

575.19

479.52

11.27

592.76

494.16

11.90

17.57

14.64

0.63

6,400

572.72

470.01

11.67

589.43

483.71

11.66

16.71

13.70

-0.01

6,500

573.10

463.07

12.24

589.07

476.01

11.77

15.97

12.94

-0.47

6,600

570.64

454.10

12.23

592.28

471.32

12.11

21.64

17.22

-0.12

6,700

565.40

443.23

11.62

579.05

453.93

12.27

13.65

10.70

0.65

6,800

573.91

443.28

10.58

590.44

456.03

12.61

16.53

12.75

2.03

6,900

561.54

427.50

5.35

579.57

441.15

10.33

18.03

13.65

4.98

Editor's Note: Our test was done on an absolutely stifling-hot day in Southern California.